Pen recorders have been used in the past to display and record continuous signals in power plants such as temperature, voltage, power, pressure, flow load and vibration. These recorders consume large amounts of chart material and in many cases only a portion of the recording is of permanent value. In many cases the only portion of interest involves an abnormal condition such as an out of limit variable.
A cathode ray tube display which can monitor a number of variables would be useful. However, the display of signals having a long time base relative to the integration time of the human eye presents a problem. Long persistence phosphors are often used where the length of the time axis is in the order of several seconds. This type of display is not very satisfactory since only the most recent portion of the trace is well illuminated. Storage tubes have been used for displays having a long time base. They are excessively expensive and have other undesirable characteristics.
Signal time compression systems involving delay lines and shift registers have been described by Westerfield in U.S. Pat. No. 3,093,796 and Klund in U.S. Pat. No. 3,327,062. These systems involve the circulation of binary information in a shift register or delay line store. The shift register provides a convenient and inexpensive method of storing and manipulating information.
It is an object of this invention to provide a multi-channel non-fading display on an ordinary cathode ray tube or other appropriate display type monitor using information from a recirculating shift register. A further object is to provide a delayed replica of a monitored signal to a pen recorder during abnormal conditions. A further object is to permit the retention of a selected event on the cathode ray tube display. A further object is to permit the recording and display of long-term trend information. A further object is to permit the rapid transfer of said trend information to a pen recorder in order to provide a permanent record.